physics unit 3: forces

Apparent weight

weight changing with an acceleration system (such as on an elevator)

When are objects in equilibrium

When there’s zero acceleration

If a = 0 then Net force is equal to?

Net Force = 0

Acceleration is zero when

Object is at rest or is moving with constant velocity

Friction is what type of force

Parallel force

Which is greater; static coefficient or kinetic coefficient? (Test question)

Static is always greater

Kinetic friction is proportional to what force

Proportional to normal force between surfaces

Tires use what? (Test question)

Use static frictional force, as they are rolling not sliding

Terminal velocity

When an object reaches max speed as air resistance is balanced with weight

Terminal velocity and its relationship with mass and surface area

More mass = faster terminal velocity

More surface area = faster terminal velocity

2 main factors for air resistance

• how fast you’re moving (speed)

• Surface area (cross-sectional area)

Objects mass and air resistance relationship

Lighter objects are more effected by air resistance but heavier objects have more air resistance

Newton’s first law (law of inertia)

An object at rest remains at rest as long as no net force acts on it; inertia is the tendency of an object to resist any change in its motion

Two characteristics of a force

• strength, or magnitude of the force

• Direction in which the force acts

Newton’s second law

Objects acceleration is directly proportional to the force and inversely proportional to the mass

A=F/M

Newton’s third law

For every action, there is an equal and opposite reaction

Normal force is what to the surface of contact between any two objects

Perpendicular

Weight of an object is equal to

The force of gravity acting on that object (Fg)

Weight vs mass

Weight is a gravitational force; mass is the measure of an objects inertia and the amount of matter in an object (remains the same no matter the location)

Greater the force on springs

The greater the stretch or compression of the spring

Spring units

X = displacement / distance from equilibrium

K = spring constant (N/m)

What happens to force of kinetic friction when you double the normal force?

It doubles as well

Acceleration and mass

Inverse relationship

Acceleration and force

Direct relationship

acceleration on a ramp and mass

No relationship (object will have same acceleration no matter what mass)

N is equal to what

N = mg —> N = Kg * m/s²

Relationship between net force and friction

Friction reduces net force as Fnet = Fa - Ff